[PATCH] mm/vmalloc: lock contention optimization under multi-threading

rulinhuang
2024-02-07T03:29:03Z

When allocating a new memory area where the mapping address range is
known, it is observed that the vmap_area lock is acquired twice.
The first acquisition occurs in the alloc_vmap_area() function when
inserting the vm area into the vm mapping red-black tree. The second
acquisition occurs in the setup_vmalloc_vm() function when updating the
properties of the vm, such as flags and address, etc.
Combine these two operations together in alloc_vmap_area(), which
improves scalability when the vmap_area lock is contended. By doing so,
the need to acquire the lock twice can also be eliminated.
With the above change, tested on intel icelake platform(160 vcpu, kernel
v6.7), a 6% performance improvement and a 7% reduction in overall
spinlock hotspot are gained on
stress-ng/pthread(https://github.com/ColinIanKing/stress-ng), which is
the stress test of thread creations.

Reviewed-by: "Chen, Tim C" <tim.c.chen@intel.com>
Reviewed-by: "King, Colin" <colin.king@intel.com>
Signed-off-by: rulinhuang <rulin.huang@intel.com>
---
mm/vmalloc.c | 31 +++++++++++++++----------------
1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d12a17fc0c171..3b1f616e8ecf0 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1577,13 +1577,13 @@ preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node)

/*
* Allocate a region of KVA of the specified size and alignment, within the
- * vstart and vend.
+ * vstart and vend. If vm is passed in, the two will also be bound.
*/
static struct vmap_area *alloc_vmap_area(unsigned long size,
unsigned long align,
unsigned long vstart, unsigned long vend,
int node, gfp_t gfp_mask,
- unsigned long va_flags)
+ unsigned long va_flags, struct vm_struct *vm)
{
struct vmap_area *va;
unsigned long freed;
@@ -1627,9 +1627,12 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,

va->va_start = addr;
va->va_end = addr + size;
- va->vm = NULL;
+ va->vm = vm;
va->flags = va_flags;

+ if (vm != NULL)
+ vm->addr = (void *)addr;
+
spin_lock(&vmap_area_lock);
insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
spin_unlock(&vmap_area_lock);
@@ -2039,7 +2042,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
va = alloc_vmap_area(VMAP_BLOCK_SIZE, VMAP_BLOCK_SIZE,
VMALLOC_START, VMALLOC_END,
node, gfp_mask,
- VMAP_RAM|VMAP_BLOCK);
+ VMAP_RAM|VMAP_BLOCK,
+ NULL);
if (IS_ERR(va)) {
kfree(vb);
return ERR_CAST(va);
@@ -2394,7 +2398,8 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
struct vmap_area *va;
va = alloc_vmap_area(size, PAGE_SIZE,
VMALLOC_START, VMALLOC_END,
- node, GFP_KERNEL, VMAP_RAM);
+ node, GFP_KERNEL, VMAP_RAM,
+ NULL);
if (IS_ERR(va))
return NULL;

@@ -2548,14 +2553,6 @@ static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
va->vm = vm;
}

-static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
- unsigned long flags, const void *caller)
-{
- spin_lock(&vmap_area_lock);
- setup_vmalloc_vm_locked(vm, va, flags, caller);
- spin_unlock(&vmap_area_lock);
-}
-
static void clear_vm_uninitialized_flag(struct vm_struct *vm)
{
/*
@@ -2592,14 +2589,16 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
if (!(flags & VM_NO_GUARD))
size += PAGE_SIZE;

- va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0);
+ area->flags = flags;
+ area->caller = caller;
+ area->size = size;
+
+ va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0, area);
if (IS_ERR(va)) {
kfree(area);
return NULL;
}

- setup_vmalloc_vm(area, va, flags, caller);
-
/*
* Mark pages for non-VM_ALLOC mappings as accessible. Do it now as a
* best-effort approach, as they can be mapped outside of vmalloc code.

base-commit: de927f6c0b07d9e698416c5b287c521b07694cac
--
2.43.0